System and method for arc detection and intervention in solar energy systems

ABSTRACT

An arc detection and intervention system for a solar energy system. One or more arc detectors are strategically located among strings of solar panels. In conjunction with local management units (LMUs), arcs can be isolated and affected panels disconnected from the solar energy system.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 17/001,485, filed Aug. 24, 2020, which is acontinuation application of U.S. patent application Ser. No. 15/933,861,filed Mar. 23, 2018, issued as U.S. Pat. No. 10,754,365 on Aug. 25,2020, and entitled “System and Method for Arc Detection and Interventionin Solar Energy Systems,” which is a continuation application of U.S.patent application Ser. No. 14/718,426, filed May 21, 2015, issued asU.S. Pat. No. 9,927,822 on Mar. 27, 2018, and entitled “System andMethod for Arc Detection and Intervention in Solar Energy Systems,”which is a continuation application of U.S. patent application Ser. No.13/075,093, filed Mar. 29, 2011, issued as U.S. Pat. No. 9,043,039 onMay 26, 2015, and entitled “System and Method for Arc Detection andIntervention in Solar Energy Systems,” which claims the benefit of Prov.U.S. Pat. App. Ser. No. 61/446,440, filed Feb. 24, 2011, and entitled“System and Method for Arc Detection and Intervention in Large SolarEnergy Systems,” the entire disclosures of which applications areincorporated herein by reference.

COPYRIGHT NOTICE/PERMISSION

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure as it appears in the U.S. Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

FIELD OF THE TECHNOLOGY

This disclosure relates to various embodiments of solar energy systemsand more particularly to the detection of arcs within photovoltaicpanels and the isolation and disconnection of these panels from thesystems.

BACKGROUND

Solar energy systems are often plagued by arcing. In most cases, thearcing occurs inside the solar panels. This problem can affect theperformance and safety of the whole system, and it can even lead toshut-offs due to sporadic short circuits. Arcing often occurs when solarpanels have become cracked or damaged, permitting water to leak into thepanel. The presence of water may cause a short circuit of the siliconwafers to the frame or to the underlying structure, resulting in arcing.What is needed is a system and method by which an arc can be found andisolated from the rest of the system, hence improving system performanceand reducing safety risks such as the risk of fire.

SUMMARY OF THE DESCRIPTION

Embodiments of an arc detection and intervention system for a solarenergy system are disclosed. One or more arc detectors are strategicallylocated among strings of solar panels. In conjunction with systemmanagement units and local management units (LMUs), arcs can be isolatedand affected panels disconnected from the solar energy system.

These and other objects and advantages will become clear to thoseskilled in the art in view of the description of the best presentlyknown mode of carrying out the inventions and the industrialapplicability of the preferred embodiment as described herein and asillustrated in the figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The purposes and advantages of presented inventions will be apparentfrom the following detailed description in conjunction with the appendedfigures of drawings, in which:

FIG. 1 shows a representative photovoltaic system;

FIG. 2 shows the interior of a representative enhanced photovoltaicpanel;

FIG. 3 shows an overview of an photovoltaic system;

FIG. 4 shows a detailed view of a representative arc detector; and

FIG. 5 shows a testing process for detecting arcs within photovoltaicsystem.

In the various figures of the drawings, like references are used todenote like or similar elements or steps.

DETAILED DESCRIPTION

In the following description and in the accompanying drawings, specificterminology and drawing symbols are set forth to provide a thoroughunderstanding of the present invention. In some instances, theterminology and symbols can imply specific details that are not requiredto practice the invention.

FIG. 1 illustrates a representative photovoltaic system 100, accordingto one aspect of the system and method disclosed herein. Photovoltaicsystem 100 is built from a few components, including photovoltaicmodules 101 a, 101 b . . . 101 n, local management unit units 102 a, 102b . . . 102 n, an inverter 103, and system management unit 104.

In one approach, the system management unit 104 is part of the inverter103, the combiner box 106, local management units 102, or a stand-aloneunit. The solar modules 101 a, 101 b . . . 101 n are connected inparallel to the local management units 102 a, 102 b . . . 102 nrespectively, which are connected in series to form a string bus 105,which eventually is connected to an inverter 103 and the systemmanagement unit 104.

In FIG. 1 , the string bus 105 can be connected to the inverter 103directly or as part of a mesh network or combiner boxes or fuse boxes(not shown). An isolated local management unit can be used as a combinerbox 106 to adjust all voltages before connecting to the inverter 106;or, a single or multi-string inverter can be used. To limit the changesin the voltage of the bus, the system management unit 104 may assign adifferent phase for each of the local management units 102 a, 102 b . .. 102 n. In one approach, at any given time, a maximum of apredetermined number of solar modules 101 (i.e., one single solar panel)are disconnected from the string bus 105.

In one approach, beyond the panel connection, the local management unitscan have the signal inputs (not shown), including but not limited toduty cycle, phase, and synchronization pulse (for example, to keep thelocal management units synchronized). In one approach, the phase and thesynchronization pulse are used to further improve performance, but thelocal management units 102 can work without them.

In one approach, the local management units may provide output signals.For example, the local management units 102 may measure current andvoltage at the module side and optionally measure current and voltage inthe string side. The local management units 102 may provide othersuitable signals, including but not limited to measurements of light,temperature (both ambient and module), etc.

In one approach, the output signals from the local management units 102are transmitted over a power line (for example, via a power linecommunication (PLC)), or transmitted wirelessly.

In one approach, the system management unit 104 receives sensor inputsfrom light sensor(s), temperature sensor(s), one or more each forambient, solar module or both, to control the photovoltaic system 100.In one approach, the signals may also include synchronization signals.For example, using the described methods, the local management unit canbe a non-expensive and reliable device that can increase the throughputof a photovoltaic solar system by a few (for example, single or lowdouble digits) percentage points. These varied controls also allowinstallers using this type of system to control the VOC (open circuitvoltage) by, for example by shutting off some or all modules. Forexample, by using the local management units 102 of the system 100, afew modules can be disconnected from a string if a string is approachesthe regulatory voltage limit, permitting more modules to be installed ina string.

In some approaches, local management units 102 can also be used withinthe solar panel to control the connection of solar cells attached tostrings of cells within the solar panel.

FIG. 2 shows the interior of a representative enhanced solar panel 200,according to one aspect of the system and method disclosed herein, withstandard solar module 101 x and local management unit (LMU) 102 x. LMU102 x can be integrated into a junction box (Jbox) or, in some cases,into the panel 200 itself. LMU 102 x provides two connectors 112 and 114for serial connections with other local management units 102 to connectto string bus 105. The controller 109 controls the states of theswitches Q1 106 and Q2 108. When the controller 109 turns on the switch106, the module voltage and the capacitor C1 110 are connected inparallel to the connectors 112 and 114. The output voltage between theconnectors 112 and 114 is substantially the same as the output panelvoltage. During the period the switch 106 is turned off (open), thecontroller 109 turns on (closes) the switch 108 to provide a path arounddiode D1 107 to improve efficiency. While the switch 106 is open, thepanel voltage charges the capacitor C1 110, such that when the switch106 is open, both the solar module 101 x and the capacitor 110 providecurrent going through the connectors 112 and 114, allowing a currentlarger than the current of the solar panel 200 to flow in the string(the string bus 105). When the switch 106 is open, the diode D1 107 alsoprovides a path between the connectors 112 and 114 to sustain current inthe string, even if the switch 108 is open for some reason.

In one approach, the controller 109 is connected (not shown in FIG. 2 )to the panel voltage to obtain the power for controlling the switches Q1106 and Q2 108. In one approach, the controller 109 is further connected(not shown in FIG. 2 ) to at least one of the connectors to transmitand/or receive information from the string. In one approach, thecontroller 109 includes sensors (not shown in FIG. 2 ) to measureoperating parameters of the solar panel, such as panel voltage, panelcurrent, temperature, light intensity, etc.

FIG. 3 shows an overview of a representative system 300, according toone aspect of the system and method disclosed herein. System 300 hassystem management unit 104 and multiple strings 310 a-n, each stringcontaining multiple panels 101 with associated LMUs 102. Additionally,arc detectors such as, for example, 301, 302, 303, and 304 are insertedinto system 300. In some cases, only a single arc detector 301 isincluded in the entire system 300, and the location of a problem isdetermined by turning individual units on and off, as described later.In other cases, however, to speed up the process of arc detection, eachstring 310 a-n may have its own associated arc detector. In some cases,in system 300, multiple combiner boxes 106 may feed into a singleinverter 103, so different locations in the wiring of the system can bechosen for the location of the arc detector(s), depending on the designof the specific system.

FIG. 4 shows a more detailed view of a representative arc detector 400,according to the system and method disclosed herein. Arc detector 400 isjust one example of a suitable device for arc detectors 301, 302, 303,and 304. Typically, one of two main approaches is taken. A couplingdevice such as device 402 or device 403 may be inserted in the wiring401 of system 400. Device 402 is a Rogowski coil, a type of transformerthat may be clipped onto a wire, wherein the unbroken wire forms theprimary winding. Device 403 is a standard type of transformer thatrequires that the wire be cut and the device inserted into the circuit.Both devices 402 and 403 deliver an output signal to a circuit 405 ofarc detector box 404. Many such detector boxes 404 are currently knownin the art; see, for example, U.S. Pat. Nos. 6,683,766, 5,629,824,5,619,105, 5,280,404, and 5,121,282 that describe some of many possiblevarious types of arc detection circuits. In some cases, a capacitivecoupling is used to look for broad band noise that often accompany arcs.In particular, all such devices look for unusual behavior in eithervoltage changes or changes of frequency spectrum, and consider thesechanges as indicators of the presence of arcing. The arc detectioncircuit then communicates via link 406 to the system management unit104, signaling that the detector 404 has detected an arc. Systemmanagement unit 104, in response to the signal from detector 404, theninitiates a test, which is described below in the discussion of FIG. 5 .For the purposes of the system and method described herein, noparticular type should be considered better than any other type, as longas it has the capability to detect arcing in a dc circuit, as it is usedherein.

FIG. 5 shows a representative testing process 500 for detecting arcswithin a solar energy system, according to one aspect of the system andmethod disclosed herein. At point 501, the system receives a signalindicating detection of an arc and initiates the test. At step 502, thesystem evaluates the signal value; for example, depending on the arcdetection circuitry employed, different types of arcs and differentstrengths or danger levels may be indicated, rather than simply thepossible presence of an arc. In step 503, the system assembles a list ofpotentially affected panels, including the LMU numbers.

As described above, in the discussion of FIG. 3 , if arc detectors areattached individually to each of strings 310 a-n, then only panels inthe indicated string require testing. However, if the arc detectiondevice is attached to combiner box 106, then all panels in all thestrings connected to the combiner box 106 must be tested. In step 504,the system increments the unit count i to 1 and, in step 505, turns thepanel off. In step 506, the system holds the unit in an off state for aduration t, and upon the completion of duration t, in step 507, thesystem checks to determine whether the arcing signal has ceased. If thesignal has not ceased, the system moves to step 508, where it turns onpanel i, and then to step 509, where it increments the unit count i toi+1.

In step 510, the system determines whether the current count i isgreater than the number of panels u. If, at step 510, the systemdetermines that i is less than u, the system loops back to step 505 andexecutes the test on the next panel. If, at step 510, the testing hasreached a point where i is equal to or greater than u, the systemconcludes 511 that the problem lies outside the panels, perhaps in thewiring. In step 512, the system compiles a report and sends it to anenergy system service monitoring company, and in step 513, the testends. If, at step 507, the system determines that the arcing signal hasceased after testing a panel, the system notes the panel number, whichit sends to the report compiler in step 512, and then the process loopsback to step 509, where the unit number is incremented and the testingcontinued, in case some other units are also arcing.

Depending on the topology of system 300, in some cases an LMU may haveat least one additional switch (on line 112 opposite Q1, not shown) inthe LMU 102 x shown in FIG. 2 allowing to completely disconnect thesolar module 101 x from the string bus 105 (respectively connections 112and 114) to completely insulate the solar cells from the string. Inother cases, there may be only a single switch, which in some cases maynot permit complete insulation, requiring that the whole string beturned off at the combiner box, for example, for safety reasons. At thesame time, the system can notify the service company, which can thendeliver and install a replacement panel in a very short time, reducingthe energy system down-time dramatically.

In the foregoing specification and the following appended documents, thedisclosure has been described with reference to specific exemplaryembodiments thereof. It will be evident that various modifications maybe made thereto without departing from the broader spirit and scope asset forth in the following claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

While the particular system, apparatus, and method for arc detection andIntervention as herein shown and described in detail, is fully capableof attaining the above-described objects of the inventions, it is to beunderstood that it is the presently preferred embodiment of the presentinventions, and is thus representative of the subject matter which isbroadly contemplated by the present inventions, that the scope of thepresent inventions fully encompasses other embodiments which can becomeobvious to those skilled in the art, and that the scope of the presentinventions is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular means“at least one”. All structural and functional equivalents to theelements of the above-described preferred embodiment that are known orlater come to be known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the present claims. Moreover, it is not necessary for adevice or method to address each and every problem sought to be solvedby the present inventions, for it to be encompassed by the presentclaims. Furthermore, no element, component, or method step in thepresent disclosure is intended to be dedicated to the public, regardlessof whether the element, component, or method step is explicitly recitedin the claims.

What is claimed is:
 1. A system, comprising: a plurality of devices,each device in the plurality of the devices having: a switch to controloutput of electricity generated by a respective photovoltaic panel towhich the respective device is locally coupled, and a controller; and acomputing apparatus in communication with controllers in the pluralityof devices and in communication with a detector in a photovoltaic systemhaving photovoltaic panels controlled by the plurality of the devices,wherein in response to the detector detecting an arc fault in thephotovoltaic system, the computing apparatus communicates with thecontrollers to change operations of the photovoltaic panels.
 2. Thesystem of claim 1, wherein the changes in the operations of thephotovoltaic panels include turning off output of a subset of thephotovoltaic panels to cause the detector to report absence of the arcfault in the photovoltaic system.
 3. The system of claim 2, whereinoutput of the subset of the photovoltaic panels is turned off for apredetermined period of time in accordance with communications betweenthe computing apparatus and the controllers; and arc fault results ofthe detector during the predetermined period of time are used to infer alocation of the arc fault.
 4. The system of claim 1, wherein the changesin the operations of the photovoltaic panels include turning off outputof the photovoltaic panels one at a time to identify a photovoltaicpanel turning off which causes the detector to report a change indetection results in the photovoltaic system.
 5. The system of claim 4,wherein the computing apparatus infers a location of the arc fault basedon the change in detection results in the photovoltaic system.
 6. Thesystem of claim 1, wherein the changes in the operations of thephotovoltaic panels include turning off output of the photovoltaicpanels one subset at a time; and the computing apparatus infers alocation of the arc fault based on correlations between changes indetection results of the detector and the changes in the operations ofthe photovoltaic panels.
 7. The system of claim 1, further comprising:the detector, wherein the arc fault is detected based on a signal in aset of wires in the photovoltaic system, wherein the signal correspondsto one or more of a voltage change and a frequency spectrum change. 8.The system of claim 7, wherein the arc fault includes broad band noisethat accompanies an arc.
 9. The system of claim 1, wherein the computingapparatus identifies a location of the arc fault within the photovoltaicsystem based on responses of the detector as results of changes in theoperations of the photovoltaic panels.
 10. A method, comprising:controlling, by a plurality of devices, a plurality of photovoltaicpanels, wherein each device in the plurality of the devices has: aswitch to control output of electricity generated by a respectivephotovoltaic panel to which the respective device is locally coupled,and a controller; and communicating, by a computing apparatus, with thecontrollers in the plurality of devices and with a detector in aphotovoltaic system having the photovoltaic panels controlled by theplurality of the devices; and detecting, by the detector, a presence ofan arc fault in the photovoltaic system, in response to the detectordetecting the presence of the arc fault in the photovoltaic system:instructing, by the computing apparatus via the communicating, thecontrollers to change operations of the photovoltaic panels.
 11. Themethod of claim 10, wherein the changes in the operations of thephotovoltaic panels include turning off output of a subset of thephotovoltaic panels to cause the detector to report absence of the arcfault in the photovoltaic system.
 12. The method of claim 11, whereinoutput of the subset of the photovoltaic panels is turned off for apredetermined period of time in accordance with communications betweenthe computing apparatus and the controllers; and the detecting resultsof the detector during the predetermined period of time are used toinfer a location of the arc fault.
 13. The method of claim 10, whereinthe changes in the operations of the photovoltaic panels include turningoff output of the photovoltaic panels one at a time to identify aphotovoltaic panel turning off which panel causes the detector to reporta change in detection results in the photovoltaic system.
 14. The methodof claim 13, wherein the identifying of a location includes inferringthe location of the arc fault based on the change in detection resultsin the photovoltaic system.
 15. The method of claim 10, wherein thechanges in the operations of the photovoltaic panels include turning offoutput of the photovoltaic panels one subset at a time; and theidentifying of a location includes inferring the location of the arcfault based on correlations between the changes in the detection resultsof the detector and the changes in the operations of the photovoltaicpanels.
 16. The method of claim 10, further comprising: detecting, bythe detector, the arc fault based on a signal in a set of wires in thephotovoltaic system, wherein the signal corresponds to one or more of avoltage change and a frequency spectrum change.
 17. The method of claim16, wherein the arc fault is representative of broad band noise thataccompanies an arc.
 18. The method of claim 10, further comprising:receiving, in the computing apparatus via the communicating, detectingresults from the detector responsive to changes in the operations of thephotovoltaic panels; and identifying, by the computing apparatus, alocation of the arc fault within the photovoltaic system based onchanges in detecting results responsive to the changes in the operationsof the photovoltaic panels.
 19. An apparatus, comprising: a computingapparatus in communication with controllers in a plurality of devicesand in communication with a detector in a photovoltaic system having aplurality of photovoltaic panels controlled by the plurality of thedevices, wherein each device in the plurality of the devices has: aswitch to control output of electricity generated by a respectivephotovoltaic panel to which the respective device is locally coupled,and a controller; and wherein in response to the detector detectingpresence of an arc fault in the photovoltaic system, the computingapparatus communicates with the controllers to change operations of thephotovoltaic panels.
 20. The apparatus of claim 19, wherein the changesin the operations of the photovoltaic panels include turning off, for apredetermined period of time, output of the photovoltaic panels onesubset at a time to identify changes in detecting results of thedetector caused by turning off output of one or more subsets of thephotovoltaic panels.